Radiation pickup device incorporating electron multiplication

ABSTRACT

An electronic image pickup device for detecting a radiation image and providing an electrical output corresponding to said radiation image. The pickup tube incorporates a photocathode responsive to input radiation for generating an electron image which is directed through a channel electron multiplying structure for multiplying the electron image and a storage member is incorporated into the output of said channel multiplier to provide a charge image which can be readout by electronic means. In addition, the structure disclosed provides a combination microchannel multiplier and storage electrode which permits either destructive or nondestructive readout of the stored image by the reading electron beam.

United States Patent Peter R. Collings;

[72] Inventors R011 R. Beyer, Horseheads, N.Y.

[21] AppLNo. 819,021

22 Filed Apr. 24, 1969 [45] Patented Jan. 12, 1971 [731 AssigneeWestinghouse Electric Corporation Pittsburgh, Pa.

a corporation of Pennsylvania [54] RADIATION PICKUP DEVICE INCORPORATINGELECTRON MULTIPLICATION 7 Claims, 3 Drawing Figs.

[52] U.S.Cl 315/11, 313/68, 313/103 [51] lnt.Cl H0lj3l/48 [50] Fieldot'Search 313/103, 104, 68; 315/11, 12

[56] References Cited UNITED STATES PATENTS 3,440,470 3/1969 Decker313/103 Primary ExaminerRodney D. Bennett, Jr.

' Assistant ExaminerJoseph G. Baxter Attorneys-F. H. Henson and C. F.Renz ABSTRACT: An electronic image pickup device for detecting aradiation image and providing an electrical output corresponding to saidradiation image. The pickup tube incorporates a photocathode responsiveto input radiation for generating an electron image which is directedthrough a channel electron multiplying structure for multiplying theelectron image and a storage member is incorporated into the output ofsaid channel multiplier to provide a charge image which can be readoutby electronic means. In addition, the structure disclosed provides acombination microchannel multiplier and storage electrode which permitseither destructive or nondestructive readout of the stored image by thereading electron beam.

llllllllllllllllllllllllllIlll l I l l RADIATION PICKUP DEVICEINCORPORATING ELECTRON MULTIPLICATION BACKGROUND OF THE INVENTION Thechannel multiplier is an electron multiplier which consists of a body orplate of insulating material having opposite major faces provided withelectrically conductive layers and channels or openings in theinsulating material and extending between these major faces. Theinterior surface of the chan nels is a secondary emissive material. Thesecondary emissive material may be provided in the form' of a coating.Primary electrons entering the channel bombard this secondary emissivecoating and thereby create a substantial larger number of secondaryelectrons emitting from the opposite face than incident primaryelectrons. The channel multipliers have found application in direct viewimage intensifier tubes and are particulariy advantageous in high gainstructures. It has also been suggested that such a microchanne] plateamplifier could be used as a means of pretarget signal amplificationwithin an intensifier camera tube. In this type of device,photoelectrons liberated by an optical image focused on asemitransparent photocathode are accelerated toward and focused upon thefront surface of a microchannel plate. The photoelectrons entering thechannels of the microchannel plate are multiplied in the usual mannerand electrons issue from the exit surface of the microchannel and areagain accelerated and refocused upon a storage target where they may befurther multiplied and stored until readout by the scanning. readingbeam of a conventional camera tube reading section.

There are severaldisadvantages to this type of pickup tube. The mostimportant of which is the loss of contrast and the limitation ofresolution which accompanies a transfer of an electron image from amicrochannel plate multiplier to the storage target. focusing mechanismemployed to convey the electron image may be either magnetic,electrostatic or proximity focusing. The latter is the means mostcommonly employed since the weight and space requirements of the twoconventional focusing methods are usually prohibitive. However, forproper proximity focusing the 'microcharmel plate must beplaced veryclose to the storage target and very high SUMMARY OF THE INVENTION Thisinvention is directed to an improved electron image pickup tube whichincorporates pretarget multiplication in the form of a microchannelplate type multiplier and in which the storage target is formedon themicrochannel plate itself.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional view of anelectron imaging device incorporating the teachings of this invention;

FIG. 2 is an enlarged sectional view of a portion of the microchannelamplifier storage plate incorporated in FIG. 1; and

FIG. 3 illustrates a modified microchannel multiplier storage electrodewhich may be incorporated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring in detail to FIG. 1,an electron imaging pickup tube is illustrated which includes anevacuated envelope 10.

, Theenvelope includes an enlarged tubular portion 12 which is referredto as the electron imaging section and a smaller tubular body portion 14in which a reading gun 16 is positioned and may be referred to as thereading section of the envelope. The tubular portions 12 and 14 areconnected together and the portion 12 is provided with an input window18 closing the opposite end through which the input radiations aredirected. The opposite end of the tubular section 14 is closed off by abase portion 20 through which suitable leads (not shown) are providedfor application of suitable potentials to the electrodes within theelectron gun 16.

The electron gun 16 is of suitable design to provide a low velocityscanning electron beam which is directed onto a channel multiplierstorage electrode 22. The electron gun 16 includes at least a cathode24, a control grid 26 and an anode 28. An alignment coil 30, a focusingcoil 32 and suitable deflection coils 34 are provided about the tubularportion 14 to provide suitable focusing and deflection of the electronbeam generated by the electron gun 16. In this manner the electron beammay be scanned in a suitable raster over the output side of theelectrode 22.

The input radiation is directed through the input window 18 onto asuitable photoemissive layer 40 which generates photoelectrons inresponse to excitation by the input radiations. The photoelectronsemitted by the photocathode 40 are directed through a suitable electronimaging system 42 onto the input side of the electrode 22.

Referring in detail to FIG. 2 which shows the details of the electrode22, the electrodeconsists of a fiat plate 50 of a suitable insulatingmaterial such as glass having channels 52 passing through the insulatingplate from the entrance or input surface 54 to the exit or outputsurface 56. The plate 50 may have a thickness of about 0.05 inch and thediameter of the channels may be about 0.001 inch. The inner surface ofthe channels 52 are treated or provided with a suitable coating toprovide a surface that emits secondary electrons of greater number thanincident primary electrons. This secondary emissive surface is indicatedas 58. A more complete description of a suitable structure for themember 50 and the secondary emissive surface is given in US. Pat.3,34l-,730. The surface or coating 58 provides a coating of aresistivity of about 100 megohms to permit current flow. An electricallyconductive coating 60 of a suitable material such as gold is depositedon the entrance surface 54 and is in electrical contact with theinsulating coating 58..The electrode 60 on the entrance surface 54 isconnected to the exterior of the envelope by lead-in 61 and is providedwith a suitable potential of about 1000 volts negative with respect toground. The exit surface of the electrode 50 is also provided with aconductive coating 62 which extends back into each of the channels 52for a distance equal to about 2 channel diameters. The electrode 62 isalso brought out to the exterior of the envelope by lead-in 63 and issupplied with a potential of about ground. In addition, a coating 64 ofa suitable insulating material is provided on the exit surface 56. Thecoating 64 extends over the entire conductive coating 62. The coating 64may be of a suitable insulating material and of thickness of about 1micrometer. A control grid is provided between the exit :surface of theelectrode 22 and the reading electron gun 16. The grid 70 is connected vto the exterior of the envelope 10 by lead-in 65 to a potential of about20 volts. The coatings 62 and 64 may be deposited by any suitabletechnique such as sputtering or evaporation.

In the operation of the pickup tube shown in FIGS. 1 and 2, radiationfrom a scene is focused onto the photosurface 40 which emits electronswhich are in turn accelerated by a potential between the photocathode 40and the electrode 22 of about 5,000 volts. The electron image emittedfrom the photocathode 40 is focused by suitable means 42 onto theelectrode 22. These photoelectrons strike the walls of the channels 52and cause emission of secondary electrons from the inner surfaces 58.The microchannel electrode structure is provided with a more positivepotential on the electrode 62 with respect to the electrode 60 andbecause of the conductivity of the surface 58 within each of thechannels 52 a small current referred to as a strip current flow from theelectrode 60 to the electrode 62. in this manner, a uniform potentialgradient is established along the channel 52 which tends to acceleratethe electrons within the channel 52 toward the exit surface 56. Thisfield accelerates the secondary electrons emitted from the surface 58and continuing multiplication in this manner is obtained within thechannel as the secondary electrons continue to strike the surface 58 intheir path along the channel 52 to create further secondary electronsand thus obtain an amplified electron image within the channels 52. Thefinal impact of the secondary electrons moving down the channels 52takes place on the insulating film surface 64. As before, secondaryelectrons are produced, but in this case providing that the secondaryelectrons arriving at the insulating film 64 have sufficient energy, alarger number of secondaries will be emitted than electrons incident onfilm 64. This will tend to charge the insulating film 641 in a positivedirection in that electrons cannot flow through the insulating film 64to neutralize the positive charge. The insulating film 64 should be of amaterial with high secondary emission coefficient such as potassiumchloride, magnesium oxide, sodium bromide, sodium chloride. Under normalmicrochannel plate operating potentials, that is, 800 to 3000 volts, thesecondary electrons will arrive at the insulating surfaces 64 with anenergy above the first crossover potential. In this manner, a chargeimage is established on the insulating surface 64 proportional to theinput radiation.

This charge image established on the insulating surface 64 may be readout by the use of the reading electron beam generated by the electrongun 16. This beam is focused on the exit surface 56 of the microchannelstorage electrode 22 and impinges on the layer 64. The beam is scannedacrom the surface 56 to form a television raster with the gun cathode 24operating at near ground potential. The electrons will land only on thepositively charged areas on the storage surface 64 discharging it toground. This discharge will generate a capacitive discharge current in aload resistor 71 which is connected to the lead-in 65 and electrode 62to thus derive a video signal through a capacitor 69 representative ofthe charge image on the electrode 22.

In the structure illustrated in FIG. 2, the electrode 70 is necessary tocontrol the maximum voltage excursion on the surface of the insulatingfilm 64. FIG. 3 illustrates a modified structure which may beincorporated into FIG. 1 and eliminates the necessity of the controlmesh 70. In addition, the structure shown in FIG. 3 permits the readingelectron beam from the electron gun 16 to readout the charge image in anondestructive manner so that the spatial charge pattern continues togenerate the same video signal from one frame to another. In otherwords, the arrangement shown in FIG. 3 would provide the additionalfacility of multicopy readout. The arrangement in MG. 3 also may beswitched from the multicopy readout or nondestructive readout todestructive readout as described with respect to FIG. 2.

Referring in detail to HG. 3, the structure shown is identical to thatin FIG. 2 with the exception of an additional conductive coating 66 of asuitable material such as gold which is evaporated onto the insulatingcoating 64 but only on the portion of the insulating coating 64 on thesurface 56 of the microchannel structure. Minimum penetration of theconductive layer 66 into the channel openings 52 is provided. Aelectrical lead-in 73 is brought out from the conductive coating 66. Thelead-in 63 is connected to a suitable switch 72 for selectiveapplication of two voltages volts negative or ground. A switch 74 isalso provided for selective coupling the output to either lead-in 63 or73. A switch 76 is also provided for selective application of suitablevoltages, such as 10 volts positive and 0.5 volt negative to the lead-in73.

The operation of the arrangement shown in FIG. 3 in multicopy readoutmay be described in three phases, namely, exposure, read and erasure. Inthe exposure operation, the reading beam may be cutoff. The frontsurface electrode 61) may be at a 1000 volts negative, the exit surfaceelectrode 62 at ground potential and the electrode 66 at a 10 voltspositive. The input radiation directed onto the photocathode 4t) againgenerates photoelectrons which are focused onto the electrode 22 andimpinge on the surfaces withinfthe microchannels 52. Thesephotoelectrons will be multiplied in the usual manner and will create apositive charge pattern on the surface of the insulating coating 64 in asimilar manner as that described with respect to FIG. 2. The potentialdistribution on the insulating film surface 64 will vary between groundand +l0 depending on the current incident upon each incident upon eachindividual microchannel 52 and assuming the crossover potential for theinsulator is'greater than l0 volts.

In the read operation, the reading beam from the gun 16 is turned onwith the cathode at approximately ground potential. The image section iscutoff or the lens is capped. The exit surface electrode 62 is switchedto a 10 volts negative and the electrode 66 is switched to 0.5 voltpositive. Due to capacitive coupling, the potential of the surface ofthe insulating layer 64 is decreased by about 9.5 volts and the positivepotential pattern previously existing on the insulating film 64 nowbecomes a reversed potential pattern with potentials varying from groundto l0 volts This negative potential pattern will modulate or regulatethe amount of the scanning beam current landing on the electrode 66 withthe switch 74 connected to the lead-in 73, a video signal is thuscontinuously generated in the electrode 66 without destroying or erasingthe original charge pattern on the insulating coating 64.

In the erase operation, the exit surface electrode 62 is switched toground potential, the signal electrode 66 is switched to +10 volts andthe scanning beam is turned on In this operation, the scanning beamlands on the positive charge pattern on the insulating surface 64 so asto charge the insulating surface to substantially ground potential. Ifthe switch 74 is moved to lead-in 63, the video signal is now taken fromthe exit surface electrode 62, and destructive readout is obtained andthe electrode 66 now acts as simply a control electrode.

It is obvious from the above description that the electrical andmechanical problems associated with the camera tube prior art design isconsiderably simplified by the above structures. The resulting structurealso provides improved contrast transfer and improved resolution.Further, the facility of multicopy readout as provided in the deviceshown in FIG. 3 provides a very important new property in microchannelelectron discharge devices and considerably broadens the field ofpotential application of this device.

We claim:

1. An electron imaging device comprising a channel electron multiplierresponsive to input radiations for generating and amplifying electronsalong individual channels within said electron multiplier, said channelmultiplier including an input surface onto which input radiations aredirected and an output surface from which an output signal correspondingto said input radiations as amplified by said channel multiplier isderived and means for directing a reading electron beam over said outputsurface to derive asignal representative of said input radiationsamplified by said channel multiplier.

2. An electron image device comprising a channel electron multiplierresponsive to input radiations for generating and amplifying electronsalong individual individual channels within said electron multiplier,said channel multiplier including an input surface onto which said inputradiations are directed and an output surface from which an outputsignal is derived and means for scanning a reading electron beam oversaid output surface to derive a signal representative of said inputradiations amplified by said channel multiplier, said output surface ofsaid channel multiplier including a first conductive coating providedover the output surface and extending into each of said channels for aminor distance and a coating of insulating material provided on saidfirst electrically conductive coating on the output surface andextending into said channels so as to cover said first conductivecoating therein.

3. The device set tomb in claim 2 in which a. second electricalconductive coating is provided over a portion of the surface of saidinsulating coating.

4. The device set forth in claim 2. in which electrons directed alongeach of said channels by'a potential gradient along said channelsaccelerates said electrons and bombard said insulating coatingprojecting into said channel multipliers and thereby establish achargeimage on the surface of said insulating coating which may be read out bymeans of said reading electron beam.

5. The device set forth in claim 3 in which the electrons generatedwithin said channel multipliers are accelerated into bombardment withsaid insulating coating and thereby establishing a charge image on theinsulating coating projecting into each of said channel multipliers,means for establishing suitable potentials on said first an and secondconductive coatings and said insulating coating such that the scanningelectron beam will be modulated by the charge on said insulating coatingand collected by said second conductive coating to thereby derive anelectrical signal without destroying the charge image on said insulatingcoating.

' 6. The device set forth in claim 3 in which means is provided foroperating said first conductive coating and said second conductivecoating and said insulating coating at suitable potentials so as topermit said reading electron beam to impinge on said insulating coatingin an amount corresponding to the charge image thereon and means forderiving a signal from said first conductive coating in which saidcharge image is destructively read out therefrom.

7. The device set forth in claim 1 in whicn means is provided forconverting said input radiation into electrons which are in turnaccelerated into incidence with the channels within said channelmultiplier.

1. An electron imaging device comprising a channel electron multiplierresponsive to input radiations for generating and amplifying electronsalong individual channels within said electron multiplier, said channelmultiplier including an input surface onto which input radiations aredirected and an output surface from which an output signal correspondingto said input radiations as amplified by said channel multiplier isderived and means for directing a reading electron beam over said outputsurface to derive a signal representative of said input radiationsamplified by said channel multiplier.
 2. An electron image devicecomprising a channel electron multiplier responsive to input radiationsfor generating and amplifying electrons along individual individualchannels within said electron multiplier, said channel multiplierincluding an input surface onto which said input radiations are directedand an output surface from which an output signal is derived and meansfor scanning a reading electron beam over said output surface to derivea signal representative of said input radiations amplified by saidchannel multiplier, said output surface of said channel multiplierincluding a first conductive coating provided over the output surfaceand extending into each of said channels for a minor distance and acoating of insulating material provided on said first electricallyconductive coating on the output surface and extending into saidchannels so as to cover said first conductive coating therein.
 3. Thedevice set forth in claim 2 in which a second electrical conductivecoating is provided over a portion of the surface of said insulatingcoating.
 4. The device set forth in claim 2 in which electrons directedalong each of said channels by a potential gradient along said channelsaccelerates said electrons and bombard said insulating coatingprojecting into said channel multipliers and thereby establish a chargeimage on the surface of said insulating coating which may be read out bymeans of said reading electron beam.
 5. The device set forth in claim 3in which the electrons generated within said channel multipliers areaccelerated into bombardment with said insulating coating and therebyestablishing a charge image on the insulating coating projecting intoeach of said channel multipliers, means for establishing suitablepotentials on said first an and second conductive coatings and saidinsulating coating such that the scanning electron beam will bemodulated by the charge on said insulating coating and collected by saidsecond conductive coating to thereby derive an electrical signal withoutdestroying the charge image on said insulating coating.
 6. The deviceset forth in claim 3 in which means is provided for operating said firstconductive coating and said second conductive coating and saidinsulating coating at suitable potentials so as to permit said readingelectron beam to impinge on said insulating coating in an amountcorresponding to the charge image thereon and means for deriving asignal from said first conductive coating in which said charge image isdestructively read out therefrom.
 7. The device set forth in claim 1 inwhich means is provided for converting said input radiation intoelectrons which are in turn accelerated into incidence with the channelswithin said channel multiplier.